That's right, you can tune up your mandolin, right here on the Internet. Handy if you don't have an electronic tuner. Isn't technology wonderful?
It's best to start with the lowest-pitched string (the G) first and work your way up from there. It's also better to be a little flat and have to tune up to the correct note than to have your mando tuned too high. If your mandolin is noticeably sharp, that means the strings are too tight, which is hard on strings and on the head and neck of your instrument.
Here are MIDI files for standard GDAE tuning for mandolins:
Simple Gifts Mandolin Tablature Archive | Elizabeth T. Knuth's Home Page
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Tune Your Mando Online / Rev. 11 December 1998 / © Copyright 1998, Elizabeth T. Knuth / URL: http://www.users.csbsju.edu/~eknuth/mandotab/gdae.html